Fig. 1. Survivin concentrates near centromeres in G2 and forms an extendable bipartite structure between the sister kinetochores in mitosis. (A) Accumulation of survivin-GFP adjacent to centromeres of early G2 cells. See text for details. The arrow and arrowheads denote the midbody and the spindle poles, respectively. The merge shows overlay of survivin-GFP (green) and autoimmune anti-centromere marker (red). The insets show higher magnification of selected areas. (B) Aurora B does not co-localize with survivin-GFP foci (thin arrows) until M phase (short arrows). (C) Survivin (red) undergoes extensive stretching between the sister kinetochores (anti-hCdc20, green) in a manner dependent on microtubule attachment and chromosome bipolarity. The arrows indicate a gap separating the two survivin accumulations on chromosomes that are under robust tension. (a) prophase, (b) unattached prometaphase, (c) attached prometaphase, (d) metaphase, (e) metaphaseanaphase transition. The numbers show the average length of the survivin segments under each condition (n=10-20 chromosomes per each category). The three linescan graphs show the average gray values for the above prometaphase (f), metaphase (g), and metaphase-anaphase transition (h) chromosomes (red survivin; green kinetochores). (D) Aurora B kinase associates with survivin-GFP in mitotic HeLa cells. Immunoprecipitations were performed with rabbit anti-GFP antibody utilizing HeLa cell populations expressing either survivin-GFP or control GFP alone. The arrow denotes a 42 kDa band detected with anti-hAurora B antibody and the asterisk the antibody heavy chain at 55 kDa. IP, immunoprecipitate; S, supernatant. Bars = 10 µm (panels A,B) and 0.5 µm (panel C).